The present invention refers to a device for successively transporting sheets in a platen press. It comprises gripper bars, having respective ends which are fixedly attached to two flexible elements in the shape of endless loops. Each loop is engaged respectively with an intermittent drive wheel and at least one free wheel. A rectangular working chase and a movable platen are arranged on both sides of the path of the grippers of the bar. Nozzles connected to a compressed air supply direct air jets towards the movable platen during the stopping phase of the gripper bar, in order to successively stop the sheets between the working chase and the movable platen.
To transport a sheet, the gripper bar seizes it at the front edge and brings it between the working chase and the cutting plate fixed on the movable platen of the platen press. At the end of the path, the gripper bar strongly decelerates before stopping and is raised as soon as it comes out from the transverse rear edge of the working chase.
During this abrupt deceleration of the gripper bar, it is important to prevent deformation of the sheet and to force the sheet to remain practically flat. When a flexible sheet thus transported undergoes a strong deceleration, it primarily deforms downwards due to the force of gravity exerted on it. That is the reason why the grippers of the gripper bar are preferably located at the level of the lower face of the profile forming the gripper bar, so that the sheet travels as near as possible to the movable platen.
To avoid upward deformation of the decelerated sheet, it has already been proposed to form a flow of compressed air between the sheet and the board fixed inside the working chase of the platen press. However, in solutions suggested up to now, the nozzles that blow compressed air are arranged behind the transverse rear edge of the working chase, so that the air flow is interrupted before the grippers fully stop. Consequently a relatively large space still separates the platen from the working chase. Therefore, the air blower stops before the sheet and the space which remains at this moment between the working chase and the movable platen does not exclude further deformation of the sheet under the effect of the strong deceleration.